Person identification system

ABSTRACT

A person identification device  100  has a tag  110  with a code and a tamper evident tether  120  able to secure the tag  110  to a person having a body. The person identification device also has a signal generator  140  able to generate a signal representing the code. The tag  110  has a capacitive contact  130  able to capacitively couple the signal into the body of the person.

The invention relates to a person identification system. Morespecifically, but not exclusively, the invention relates to identifyinga person whose behaviour is being monitored and optionally controlled.

Various techniques are known for remotely identifying a person, forexample, the identity of a person may be verified by the use of a secretquestion or a pin code. However, these methods have the drawback thatthe secret question or pin code can become known or deliberately givento, and used by, an unauthorised person to circumvent behaviouralcontrol. Other methods include voice verification, facial recognition,or fingerprint recognition. However, these techniques can be unreliable,for example, facial recognition may fail if the person is wearing a hator glasses. In other techniques, images may be monitored by a humanoperator, however, this technique is slow and prone to human error.

Hence, it would be advantageous to be able to reliably and efficientlyconfirm the identity of a person in a manner than is less easilycircumvented.

The invention utilizes a signal transmitted through the human body of aperson to allow recognition and identification of the person, which ismore reliable than measuring physical features of the person, forexample, with this system, it would be impossible for identical twins tobe mixed up despite them having identical physical features, as thesignal transmitted through the body identifies the particular twin.

According to a first aspect of the invention, there is provided a personidentification device.

The person identification device comprises a tag having a code. A tamperevident tether is able to secure the tag to a person having a body. Asignal generator is able to generate a signal representing the code. Thetag has a capacitive contact able to capacitively couple the signal intothe body of the person. The fact that the signal representing the codeis capacitively coupled to the body means that the signal, and thereforethe code, may be detected all over the body of the person, for example,the code may be detected at a monitoring unit or detector the person istouching. The code uniquely identifies the tag and the use of a tamperevident tether prevents the person from removing the tag and giving itto somebody else. Hence, the code uniquely identifies the person. Thetamper evident tether also prevents somebody from stealing the tag fromthe person. The fact that the tag uses capacitive coupling to the bodyis advantageous because no signal is transmitted through free spacewhich improves privacy and security, and it also improves identificationreliability because the identification is personal to the person wearingthe tag. In other words, it can be more reliably determined that theperson interacting with a device, such as a monitoring unit, is theperson who is wearing the tag.

In exemplary embodiments, the capacitive contact comprises a conductingmaterial, e.g. one of: copper, silver or gold.

In exemplary embodiments, the conducting material comprises a sheet ofconducting material.

In exemplary embodiments, the capacitive contact comprises a compositeof the conducting material and a non-conducting material, e.g. particlesof metal dispersed in the non-conducting material.

In exemplary embodiments, the capacitive contact is on a body facingsurface of the tether or the tag. In alternative embodiments, thecapacitive contact is beneath a body facing surface of the tether or thetag.

In exemplary embodiments, the capacitive contact is covered with a layerof non-conducting material, e.g. one of: glass, plastic orpolycarbonate. In exemplary embodiments, the layer of non-conductingmaterial has a thickness of no more than 1 mm.

In exemplary embodiments, the code is represented by a modulated signal,e.g. modulated according to on-off keying. In exemplary embodiments, themodulated signal has a frequency of between 50 kHz and 300 kHz, e.g. 125kHz.

In exemplary embodiments, the signal is coupled into the body at aregular time interval.

In exemplary embodiments, the code is encrypted.

In exemplary embodiments, the signal generator comprises an LC resonantcircuit, e.g. driven by one of: a full-bridge driver; or a half-bridgedriver.

In exemplary embodiments, the capacitive contact is able to receive afurther signal capacitively coupled from the body of the person. Inexemplary embodiments, the person identification device furthercomprises a mixer to convert the frequency of the further signal. Inexemplary embodiments, the further signal instructs the personidentification device to couple the signal into the body. In exemplaryembodiments, the further signal has a frequency of between 5 MHz and 20MHz.

In exemplary embodiments, the person identification device is powered bya battery.

According to a second aspect of the invention, there is provided amonitoring unit or detector. A capacitive contact is able tocapacitively couple a signal from a body of a person. A receiver isconfigured to receive, from the capacitive contact, a signalrepresenting a code. A controller is configured to determine the codefrom the signal. The fact that the monitoring unit uses capacitivecoupling from the body is advantageous because no signal is transmittedthrough free space which improves privacy and security, and it alsoimproves identification reliability because the identification ispersonal to the person wearing the tag. In other words, it can bereliably determined that the person interacting with the monitoring unitis the person who is wearing the tag and not merely someone who isstanding nearby. The monitoring unit may be a detector which is able todetect or receive a signal capacitively coupled from a body of a person.The monitoring unit may then send the code to another device. Amonitoring unit may be a device which has other functions, for example,the monitoring unit may use the code to identify the person and/or themonitoring unit may authorise the person to perform an action.

In exemplary embodiments, the controller is further configured tocompare the code against a code database. In exemplary embodiments, thecode database is located in either: a memory or a storage device of themonitoring unit; or a remote server with which the controller is able tocommunicate. In exemplary embodiments, the comparing the code against acode database determines the identity of the person. In exemplaryembodiments, the controller is further configured to send the identityof the person to a monitoring centre. In exemplary embodiments, thecontroller is further configured to store a log of codes and thecorresponding identity of the person.

In exemplary embodiments, in the event that the monitoring unit fails todetermine the identity of the person, an alarm condition is triggered.

In exemplary embodiments, the monitoring unit further comprises a cameraconfigured to capture an image or video of the person. In exemplaryembodiments, the image or video of the user captured by the camera isused to verify the identity of the person.

In exemplary embodiments, the signal representing the code isrepresented by a modulated signal, and wherein the monitoring unitfurther comprises a demodulator to determine the code from the signal.In exemplary embodiments, the modulated signal is modulated according toon-off keying. In exemplary embodiments, the modulated signal has afrequency of between 50 kHz and 300 kHz, e.g. 125 kHz.

In exemplary embodiments, the monitoring unit further comprises anamplifier to amplify the signal.

In exemplary embodiments, the capacitive contact is able to capacitivelycouple a further signal into the body of the person. In exemplaryembodiments, the further signal instructs a person identification deviceto couple the signal into the body. In exemplary embodiments, thefurther signal has a frequency of between 5 MHz and 20 MHz.

In certain embodiments, the monitoring unit is a telephone able toreceive a code from the person using the telephone to make a voice callto a further person or receive a voice call from a further person, forexample when monitoring a prisoner on parole. The capacitive contact maybe disposed within a handset of the telephone, such that when the userholds the phone to make a voice call, a hand of the user makes contactwith the capacitive contact. The advantage of using capacitive couplingwith the tamper evident tether is the certainty that the person holdingthe phone is the person wearing the tag and the person is indentifiedfrom the signal.

In certain embodiments, the monitoring unit is a breathalyser able toreceive a code from the person using the breathalyser to provide aspecimen of breath. The monitoring unit may have a sample tubeconfigured to receive the specimen of breath from the person where thesample tube forms the capacitive contact. When the person blows into thesample tube to provide the specimen of breath, the lips of the personmake contact with the sample tube. The advantage of this is thecertainty that the person blowing into the sample tube, and thereforeproviding the specimen of breath, is the person wearing the tag that isproviding the code and hence the person is identified from the signal.

Optionally, the sample tube is made of plastic and the capacitivecontact is formed from a conducting material disposed in the plasticmaterial. The advantage of this is that it is cheap to manufacture,disposable and hygienic.

In certain embodiments, the monitoring unit is a key pad and thecapacitive contact is disposed on the surface of the key pad. The keypad may be used to receive a PIN number, for example, from a securityguard patrolling an installation who enters the PIN number into thekeypad to demonstrate that the security guard has visited a location inthe vicinity of the key pad. The fact that the key pad has a capacitivecontact means that if the security guard is wearing a tag, the identityof the security guard that visited the location can be confirmed.

In certain embodiments, the monitoring unit is an electronic door entryand the controller uses the code to determine whether to permit accessto the door.

According to a third aspect of the invention, there is provided a personidentification system. The person identification system has a personidentification device comprising a tag having a code, a tamper evidenttether able to secure the tag to a person having a body, and a signalgenerator able to generate a signal representing the code. The tag has acapacitive contact able to capacitively couple the signal into the bodyof the person. The person identification system also has a monitoringunit comprising a capacitive contact able to capacitively couple asignal from a body of a person, a receiver configured to receive, fromthe capacitive contact, a signal representing a code; and a controllerconfigured to determine the code from the signal and to compare the codeagainst a code database.

Various embodiments of the invention will now be described, withreference to the attached figures, in which:

FIG. 1 is a schematic of a person identification device according to anembodiment of the first aspect of the invention;

FIG. 2 shows the person identification device of FIG. 1 secured to aperson;

FIG. 3 shows a cross-section through the person identification device ofFIG. 1 where the capacitive contact is on a body-facing surface of thetag;

FIG. 4 shows a cross-section through the person identification device ofFIG. 1 where the capacitive contact is beneath a surface of the tag;

FIG. 5 shows a cross-section through the person identification device ofFIG. 1 where the capacitive contact comprises a composite comprisingconducting particles dispersed in a non-conducting material;

FIG. 6 shows a schematic of a circuit of a person identification device;

FIG. 7 shows a person interacting with a monitoring unit according to anembodiment of the second aspect of the invention;

FIG. 8 shows the monitoring device in more detail;

FIG. 9 shows a schematic of a circuit of the person identificationdevice of FIG. 1 or the monitoring unit of FIG. 8;

FIG. 10 shows the monitoring unit incorporated into a telephone;

FIG. 11 shows a person using the telephone of FIG. 10;

FIG. 12 shows the monitoring unit incorporated into a breathalyser; and

FIG. 13 shows a person using the breathalyser of FIG. 12.

FIG. 1 shows a person identification device 100 according to anembodiment of a first aspect of the invention. The person identificationdevice 100 comprises a tag 110 and a tamper evident tether 120. Thetamper evident tether 120 is able to secure the tag 110 to a person.

FIG. 2 shows the person identification device 100 of FIG. 1 secured tothe leg of a person. The tamper evident tether 120 could also be placedaround other parts of the person, such as around an arm or a torso ofthe person.

The tamper evident tether 120 is secured in a way that makes the personidentification device 100 difficult to remove from the person. Makingthe person identification device 100 difficult to remove may be achievedby making the tamper evident tether 120 from a material which isdifficult to cut through or break, for example, the tamper evidenttether 120 may be made from metal or a reinforced material, such as afabric containing metal fibres, or a fabric containing Kevlar, or afibre reinforced plastic material.

In addition, or alternatively, the tamper evident tether 120 may reactto tampering. For example, the tamper evident tether 120 may contain anelectrical wire, or an optical fibre, which, when cut, reports that thetamper evident tether 120 has been tampered with and may disable theperson identification device 100. The tamper evident tether 120 may alsocontain an identifier, such as an RF-ID tag, which uniquely identifiesthe tamper evident tether 120, so that attempts to remove the tamperevident tether 120 and/or to replace the tamper evident tether 120 witha different tamper evident tether may be identified by the tag 110.

Person identification devices, such as those shown in FIGS. 1 and 2, areused to confirm the identity of a person, such as a security guard, orto track and monitor people, such as offenders who are on a curfew, orprisoners, or patients who are being monitored, such as an elderly orvulnerable patient. The fact that the person identification device 100contains a tamper evident tether 120 means that the identity of theperson to which the person identification device 100 is attached can bemore reliably determined.

FIG. 3 shows a cross section through a person identification device 100.The person identification device 100 comprises a tag 110 and a tamperevident tether 120 for securing the tag to a person. The tag 110 has acapacitive contact 130 on an external surface of the tag which, when theperson identification device 100 is secured to the person, faces thebody of the person.

A signal generator 140 is able to generate a signal representing a code.The signal is coupled to the capacitive contact 130 and the capacitivecontact 130 capacitively couples the signal to the body of the person,so that the signal may be picked up at other locations on the body ofthe person.

In this embodiment, the capacitive contact is made of a sheet ofconducting material, such as a metal, for example, copper, silver orgold. In general, the capacitive contact is as large as possible as thisincreases the signal that may be coupled into the person, although, thesize of the contact may be limited by the size of the personidentification device 100 which needs to be convenient for the person towear. The capacitive contact usually has a surface area of at least 100mm².

The person identification device 100 can be secured directly to the skinof the person, with the capacitive contact 130 in direct contact withthe skin. Although typically, an air gap is allowed between thecapacitive contact 130 and the skin of the person to improve the comfortfor the person to whom the person identification device 100 is secured.The air gap attenuates the signal which is capacitively coupled to thebody of the person, so the air gap is usually less than 10 mm to allowsufficient signal to be capacitively coupled to the body, so that thesignal may be picked up at other locations on the body of the person.The strength of the signal may need to be increased to compensate forthe air gap.

Alternatively, the person identification device 100 may be secured overan item of clothing worn by the person. The item of clothing willattenuate the signal, although not as badly as an air gap having thesame thickness as the item of clothing.

FIG. 4 shows a cross section through an embodiment of a personidentification device 100 which is similar to the person identificationdevice of FIG. 3, except that the capacitive contact 430 is not on theexternal surface of the tag 110. Instead, the capacitive contact 430 inFIG. 4 is covered with a layer of non-conducing material 435.

The layer of non-conducting material 435 may be glass, plastic orpolycarbonate. The layer of non-conducting material 435 will attenuatethe signal slightly, so the non-conducting layer is thin enough (forexample, less than 1 mm) to permit sufficient signal from the capacitivecontact 430 to be capacitively coupled into the body of the person, sothat the signal may be picked up at other locations on the body of theperson.

Since an air gap between the capacitive contact 130 and the body tendsto attenuate the amount of signal which is capacitively coupled into thebody more than the presence of a non-conducting material, the personidentification device 100 is formed in a way that prevents an air gapbetween the non-conducting layer 435 and the capacitive contact 430, forexample, the capacitive contact 430 may be glued to the non-conductinglater 435, or the capacitive contact 430 may be deposited or evaporatedon top of the non-conducting layer 435.

FIG. 5 shows a cross section through an embodiment of a personidentification device where, unlike FIG. 3 and FIG. 4, the capacitivecontact 530 is not formed of a sheet of conducting material. Instead,the capacitive contact 530 in FIG. 5 is formed from a composite of aconducting and a non-conducting material, to form a composite withconducting properties. In this case, the composite comprises particlesof conducting material dispersed in the non-conducting material. Theparticles of conducting material may be metal particles, for example,particles of copper, silver or gold. The non-conducting material may beone of glass, plastic or polycarbonate.

The signal generator 140 shown in FIG. 3, FIG. 4 and FIG. 5 generates asignal which represents a code. The code is represented by the signalgenerator 140 forming a carrier signal which is modulated, for example,using an amplitude shift key modulation such as on-off keying.

FIG. 6 shows a schematic of a circuit 660 which could be used togenerate and couple the signal to the capacitive contact 630. Thecircuit 660 comprises an LC resonant circuit 662. The LC resonantcircuit 662 is driven by a driver 664, such as a full bridge or a halfbridge driver. A controller 666 generates the modulating signal whichrepresents the code stored in a memory 668.

The modulated signal has a frequency towards the lower end of the radiofrequency (RF) spectrum, typically between 50 kHz and 300 kHz. Using alow frequency RF signal is advantageous because it couples into the bodymore efficiently, thereby reducing the energy of the RF signal theperson identification device 100 must generate. This is advantageousbecause the person identification device 100 is battery powered soreducing the energy of the RF signal improves battery life and leads toa smaller lighter device because a smaller battery may be used. Inaddition, the fact that a low energy RF signal is coupled into the bodymeans that the signal cannot be detected remote from the body, therebyimproving security as the code cannot be intercepted and it can becertain that the code received by a monitoring device is coming from theperson touching the capacitive contact on the monitoring device and notfrom an external transmission.

FIG. 7 shows a person with a person identification device 100interacting with a monitoring unit 750. The person identification device100 couples a signal, representing a code, into the body of the person.A capacitive contact 730 on the monitoring unit 750 is able tocapacitively couple a signal from the body of the person.

FIG. 8 shows the monitoring unit 750 in more detail. A receiver 752 inthe monitoring unit 750 receives the signal representing the code fromthe capacitive contact 730 and passes the signal to a controller 754which determines the code from the signal.

FIG. 9 shows a schematic circuit 970 which includes the components seenin FIG. 6, which couple a signal into the body of a person, as well asadditional components which permit a signal to be coupled from the bodyof a person.

The circuit 970 comprises a capacitive contact 930, and an LC resonantcircuit 962. The LC resonant circuit 962 is driven by a driver 964, suchas a full bridge or a half bridge driver. A controller 966 generates themodulating signal which represents the code stored in a memory 968.

In addition, the circuit 970 includes components which allow the circuit970 to receive a signal capacitively coupled from the body of a person.An amplifier 972 is included to amplify the received signal which may beat a relatively low amplitude.

As mentioned previously, the person identification device 100 couples alow frequency RF signal into the body. In contrast, the monitoring unit750 couples a high frequency signal, in the range of 5 MHz to 20 MHz,into the body because it is easier to make the tag 110 smaller ifreceiving at a higher frequency So, a mixer 974 is provided todown-convert the high frequency signal into a lower frequency signalthat the controller 966 can handle. The mixer is attached to a masterclock 970. The master clock 970 may be a clock which is incorporated inthe controller 966 and therefore the frequency may be a frequency, suchas 125 kHz, which is a multiple of the controller clock frequency. Theoutput of the amplifier 972 is not impendence matched with the mixer974, so a matching network 976 is included to transform the outputimpendence of the amplifier to match the input impendence of the mixer974.

A band pass filter 978 rejects all signals other than the modulatedsignal. Certain embodiments use on-off keying modulation such that onlythe carrier of the signal needs to be passed through the band passfilter 978 which enables the band pass filter to be narrow at around orat twice the transmission baud rate, which improves noise rejection.

A demodulator 980 takes the output of the band pass filter 978 andconverts it into a digital pulse train which is passed to the controller966 to determine the code.

The circuit shown in FIG. 9 could be incorporated into a personidentification device 100 to allow the person identification device 100to both couple a signal into the body of a person, as well as to receivefurther signals which are capacitively coupled from the body of theperson, for example, signals received from a monitoring unit 750.

The circuit shown in FIG. 9 could also be incorporated into a monitoringunit 750 to permit the monitoring unit to receive a code capacitivelycoupled into the body of a person wearing a person identification device100, as well as to capacitively couple a further signal into the body ofa person, such that the monitoring unit 750 may communicate with theperson identification device 100. For example, the monitoring unit 750may capacitively couple a signal into the body which instructs theperson identification device 100 to capacitively couple the code intothe body of the person. This means that, instead of the personidentification device 100 constantly or periodically sending a signal,the person identification device 100 need only transmit the signal whenit receives a further signal from the monitoring unit 750. This is anadvantages because the person identification device 100 is a batterypowered device and continuously or intermittently coupling the signalinto the body will quickly deplete the battery of the personidentification device 100. In contrast, the monitoring unit 750 istypically either a device in a fixed location which is attached to mainselectricity, or else is a device where size and weight is less of anissue meaning the monitoring unit 750 may have a larger battery, so thepower consumption required for the monitoring unit 750 to periodicallypoll for the presence of a person identification device 100 is less ofan issue.

To prevent a third party from being able to determine the code that iscapacitively coupled into the body of the person, the code may beencrypted. The monitoring unit 750 will poll for a person identificationdevice 100 by capacitively coupling a response request which isencrypted with AES (advanced encryption standard) encryption. The personidentification device 100 in capacitive communication with the bodyreceives the response request and will decrypt the response request withan AES key stored in the memory 668 of the person identification device100. The person identification device 100 will encode a responsecontaining the code and a session key. The monitoring unit 750 willdecrypt the response and authenticate the person identification device100 based upon the session key.

The monitoring unit 750 may use the code to attempt to determine theidentity of the person to whom the person identification device 100 issecured. The controller 754 in the monitoring unit 750 compares the codeagainst a code database. The code database is located either in a memoryor storage device of the monitoring unit 750, or on a remote server withwhich the controller 754 is able to communicate. By comparing the codeagainst the code database, the controller attempts to determine theidentity of the person to which the person identification device 100 issecured.

The controller may also send the code, or information concerning theidentity of the person, to another device, for example, to permit theperson wearing the tag to perform some action, such as opening a door,or authenticating a transaction.

FIG. 10 shows a monitoring unit 750 which has been incorporated into atelephone 1000. The telephone handset 1100 incorporates a capacitivecontact 730, such as a sheet of conducting material, such as metal, forexample, copper, silver or gold. As shown in FIG. 11, when the person towhom the person identification device 100 is secured picks up thetelephone handset 1100 to make a call, the person touches the capacitivecontact 730 with their hand. The person identification device 100capacitively couples a signal containing a code into the body of theperson. The signal is coupled through their body to their hand where thecapacitive contact 730 capacitively couples the signal from their hand.The capacitive contact 730 sends the signal to the monitoring unit 750which contains a circuit, such as the circuit shown in FIG. 9, whichdetermines the code and the identity of the person. This allows theidentity of the person holding the telephone handset 1100 to beidentified and this information can be logged on the telephone ortransmitted to a monitoring centre. The fact that the code iscapacitively coupled from the person identification device 100 throughthe body of the person to the telephone handset 1100 means that theperson to whom the person identification device 100 is secured must havebeen the person holding the telephone handset 1100 at the time the callwas made, so that person must have been in the vicinity of thetelephone. The identity of the caller may be confirmed by incorporatingother identification features into the telephone 1000, for example,voice recognition or a camera to take an image of the person using thetelephone 1000.

FIG. 12 shows a monitoring unit 750 which has been incorporated into abreathalyser 1200 for determining whether a person has been consumingalcohol. The breathalyser 1200 is able to receive a code from the personwho is using the breathalyser. The breathalyzer has a sample tube 1210configured to receive the specimen of breath from the person and thesample tube 1210 comprises or forms the capacitive contact 730.

FIG. 13 shows a person using the breathalyser 1200. The person to whomthe person identification device 100 is secured places their lips aroundthe sample tube 1210 and blows into the sample tube 1210 to provide thespecimen of breath. Since the sample tube 1210 comprises or forms thecapacitive contact 730, the lips of the person make contact with thecapacitive contact 730. The person identification device 100capacitively couples a signal containing a code into the body of theperson. The signal is coupled through their body to their lips where thecapacitive contact 730 capacitively couples the signal from their lips.The capacitive contact 730 sends the signal to the monitoring unit 750incorporated into the breathalyser 1200 which contains a circuit, suchas the circuit shown in FIG. 9, which determines the code and determinesthe identity of the person. This allows the identity of the personproviding the specimen of breath to be identified and this informationcan be logged on the breathalyser or transmitted to a monitoring centre.The fact that the code is capacitively coupled from the personidentification device 100 through the body of the person to thebreathalyser 1000 means that the person to whom the personidentification device 100 is secured must have been the person whoselips were placed around the sample tube 1210 and therefore must be theperson who provided the specimen of breath.

The sample tube 1210 may be made of plastic and may also be replaceableto improve hygiene. To form the capacitive contact 730, the plasticsample tube has particles of conducting material dispersed in theplastic material. The particles of conducting material may be metalparticles, such as particles of copper, silver or gold.

In other embodiments, a monitoring unit 750 may be incorporated intoother devices where it is desirable to confirm the identity of a personinteracting with the device.

The monitoring unit 750 may be incorporated into an electronic doorentry system and the controller uses the code to determine whether topermit access to the door.

A monitoring unit 750 may be incorporated into a key pad with thecapacitive contact 730 disposed on the surface of the key pad. The keypad may be used to receive a PIN number. The fact that the key pad has acapacitive contact 730 and monitoring unit 750 means that if the personusing the key pad is wearing a tag 100, the identity of the person usingthe key pad can be confirmed. This identity information could be used toauthorise a transaction, such as at an ATM, to open or unlock a door, orto confirm that a security guard patrolling an installation has visiteda particular location.

The skilled reader will understand that the capacitive contact 730 maybe implemented in a number of different ways. For example, thecapacitive contact 730 could be a metal plate or ring. Also, thecapacitive contact 730 could be constructed from a composite material,which could also be in the form of a plate or a ring. The capacitivecontact 730 could be an integral part of a device such as a phone 1000or a breathalyser 1200 or a sample tube 1210, for example integratedwith the materials forming the device. Also, the capacitive contact 730could be in addition to the device, such as an externally fitted orretro-fit capacitive contact.

We anticipate that some uses would not need a tamper evident tether 120.

Cameras or other verification means may be used in addition to thesignal.

1. A person identification device comprising: a tag having a code; atamper evident tether able to secure the tag to a person having a body;a signal generator able to generate a signal representing the code; andthe tag having a capacitive contact able to capacitively couple thesignal into the body of the person.
 2. The person identification deviceof claim 1, wherein the capacitive contact is able to receive a furthersignal capacitively coupled from the body of the person, and wherein thefurther signal instructs the person identification device to couple thesignal into the body.
 3. The person identification device of claim 2,wherein the further signal has a frequency of between 5 MHz and 20 MHz.4. The person identification device of claim 1, wherein the capacitivecontact comprises at least one from a group consisting of a conductingmaterial, a sheet of said conducting material, and a composite of saidconducting material and a non-conducting material. 5-6. (canceled) 7.The person identification device of claim 1, wherein the capacitivecontact is either on a body facing surface of the tether or the tag, orbeneath a body facing surface of the tether or the tag.
 8. The personidentification device of claim 1, wherein the capacitive contact iscovered with a layer of non-conducting material.
 9. The personidentification device of claim 1, wherein the code is represented by amodulated signal.
 10. The person identification device of claim 9,wherein the modulated signal has a frequency of between 50 kHz and 300kHz.
 11. The person identification device of claim 1, wherein the signalis coupled into the body at a regular time interval. 12-13. (canceled)14. A monitoring unit comprising: a capacitive contact able tocapacitively couple a signal from a body of a person; a receiverconfigured to receive, from the capacitive contact, a signalrepresenting a code; and a controller configured to determine the codefrom the signal.
 15. The monitoring unit of claim 14, wherein thecontroller is further configured to compare the code against a codedatabase for determining the identity of the person, whereby theidentity of the person can be sent by the monitoring unit to amonitoring centre.
 16. (canceled)
 17. The monitoring unit of claim 15,wherein in the event that the monitoring unit fails to determine theidentity of the person, an alarm condition is triggered.
 18. Themonitoring unit of claim, further comprising a camera configured tocapture an image or video of the person.
 19. The monitoring unit ofclaim 14, wherein the signal representing the code is represented by amodulated signal, and wherein the monitoring unit further comprises ademodulator to determine the code from the signal.
 20. The monitoringunit of claim 14, wherein: the monitoring unit is a telephone configuredto receive a code from the person using the telephone to make a voicecall to a further person or receive a voice call from a further person;and the capacitive contact is disposed within a handset of thetelephone, such that when the person holds the telephone to make orreceive a voice call, a hand of the person makes contact with thecapacitive contact.
 21. (canceled)
 22. The monitoring unit of claim 20,wherein the controller is configured to store a log of voice calls andthe code received from the person making or receiving the voice call andto send the code of person making or receiving the call to the furtherperson.
 23. (canceled)
 24. The monitoring unit of claim, wherein: themonitoring unit is a breathalyser able to receive a code from the personusing the breathalyser to provide a specimen of breath; the monitoringunit has a sample tube configured to receive the specimen of breath fromthe person; and the sample tube forms the capacitive contact. 25.(canceled)
 26. The monitoring unit of claim 24, wherein the sample tubeis made of plastic and the capacitive contact is formed from aconducting material disposed in the plastic material.
 27. The monitoringunit of claim 14, wherein the monitoring unit is a key pad and thecapacitive contact is disposed on the surface of the key pad.
 28. Themonitoring unit of claim 14, wherein the monitoring unit is anelectronic door entry and the controller uses the code to determinewhether to permit access to the door.
 29. A person identification systemcomprising: a person identification device comprising: a tag having acode; a tamper evident tether able to secure the tag to a person havinga body; a signal generator able to generate a signal representing thecode; and the tag having a capacitive contact able to capacitivelycouple the signal into the body of the person; a monitoring unitcomprising a capacitive contact able to capacitively couple a signalfrom a body of a person; a receiver configured to receive, from thecapacitive contact, a signal representing a code; and a controllerconfigured to determine the code from the signal and to compare the codeagainst a code database.